1. Field of the Invention
The present invention relates to a method for recycling metals from waste catalysts, particularly to a method for recycling metals from waste tungsten catalysts by using a highly oxidized acid.
2. Description of the Related Art
In oil-refining industry, catalysts, particular to tungsten catalyst, have been widely used in hydro-desulphurization process. Generally, the tungsten catalyst has a carrier of γ-alumina, with the carrier of alumina to immobilize metals on its surfaces. Accordingly, the tungsten catalyst is easy to be ineffective due to the contamination and absorption of mass iron or phosphorus during catalysis process. Therefore, a great amount of waste tungsten catalysts are generated during the processes of oil-refining, and which may lead to serious pollutions or ecological crisis if a proper treatment of those waste catalysts has not been gone through.
Generally, waste tungsten catalysts are rich in metals, which are capable of being recycled and reused in industries. More particularly, the waste tungsten catalysts collected from various batches of hydro-desulphurization processes contains diverse composition of metals, for example, tungsten, molybdenum and nickel; tungsten and molybdenum; or tungsten and nickel; even having aluminum obtained from the surfaces of the carrier of γ-alumina. With such propose, it is a need of providing a method for recycling metals from waste tungsten catalysts, for the sake of obtaining a dramatic amount of metals from the waste tungsten catalysts and further applying recycled metals in diverse industries.
A conventional technique for recycling tungsten and molybdenum as disclosed in China Patent No. CN101824533A and entitled “METHOD FOR EXTRACTING TUNGSTEN AND MOLYBDENUM TRIOXIDE BY PRETREATING TUNGSTEN-MOLYBDENUM CONCENTRATES WITH CONCENTRATED ACID”, comprises steps of preparing by strong acid; leaching; recycling molybdenum; roasting and obtaining molybdenum trioxide, amino-soaking; condensing; cooling; roasting and obtaining tungsten trioxide, in order to extract molybdenum trioxide and tungsten trioxide from the tungsten-molybdenum concentrates.
However, the steps of the conventional technique are complicated and time-consuming, not only obtaining metals in low quality and efficiency, but being wasteful in use of acid and lye. Furthermore, the conventional technique is insufficient to recycle metals from waste tungsten catalyst due to the diversity of metals (such as nickel and aluminum) in the waste tungsten catalyst. Particularly, nickel and aluminum of the waste tungsten catalyst is difficult to be recycled or removed via sodium-roasting processes, and which may interfere with the recycling process of molybdenum and tungsten of the conventional technique. Therefore, the recycling rate, as well as the quality of recycling, of molybdenum and tungsten in the conventional technique is low and poor. On the other hand, the waste tungsten has sulfur or sulfide obtained from hydro-desulphurization processes. Sulfur or sulfide of the waste tungsten catalyst is easy to diffuse and lead to serious contamination or pollution on air or eater resource during the process in the steps of the conventional technique.
In conventional arts, there is a method to recycle metal from waste tungsten catalyst by roasting a waste tungsten catalyst at 600-900° C. for 0.5-2 hours, soaking the waste tungsten catalyst in water at 80-90° C. of hot water, and then further soaking the water tungsten catalyst in an acid to recycle nickel and cobalt and to obtain a residue after recycling. Moreover, tungsten and molybdenum can also be recycled from the residue by adding barium hydroxide or barium aluminate into the residue to obtain sodium aluminate solution, and sequentially isolating tungsten and molybdenum from the sodium aluminate solution. In this way, the recycling rate of metals in aluminum catalyst will achieve 91%.
Although the method above can effectively recycled diverse metals from waste catalyst, sulfur or sulfide will still remain in the waste catalysts and result in contamination and pollutions on air or water resource. Moreover, an additional oxidization of tungsten and molybdenum is needed for extracting tungsten and molybdenum from the waste catalysts, and however, the oxidization of tungsten and molybdenum may increase the impurity thereof and diminish the recycling rate of tungsten and molybdenum as well.
Additionally, the waste catalyst has a great amount of aluminum, with the result in interfering with the recycling of tungsten, nickel and molybdenum from the waste catalysts. In conventional arts, aluminum in the waste catalysts have to be additionally recycled by aerating carbon dioxide into the sodium aluminate solution, followed by roasting the sodium aluminate solution at a high temperature to obtain alumina. In this situation, the recycled metals only can be obtained in a time-and-cost consuming process, with poor quality and low recycling rate. It is suggested that, the conventional techniques has plenty of disadvantages and inconvenience, and therefore there is an urgent need of improving the conventional technique for recycling metals from waste catalysts.